Dawn at Vesta...

The Dawn spacecraft has been inserted into orbit around the asteroid Vesta, and this is the first (of many!) science photos to be returned (as usual, click to enlarge).  Dawn is the first spacecraft to be completely reliant on a super-efficient ion propulsion system (instead of a chemical rocket) – not so long ago, these could only be found in science fiction.  You could fairly call this mission a proof of the system's viability...